1. Field of the Invention
The present invention relates to a contactless IC card reader which reads and writes data with respect to contactless IC cards and to its data reader method; more specifically, it relates to a technology to improve data reading accuracy.
2. Description of Related Art
In recent years there has been widespread use of a contactless IC card into which an RF (Radio Frequency) IC chip and an antenna coil are built and which transmits and receives data by electromagnetic interaction via the antenna (see Unexamined Japanese Patent Application 2005-102057 (“JP 2005-102057”); and Unexamined Japanese Patent Application 2006-50406 (“JP 2006-50406”)). The reading of data recorded in contactless IC cards is not affected by dirty surfaces or wear on the cards and therefore has advantages in higher accuracy than the optical reading of data recorded in barcodes, etc.
There are three types of the above-described contactless IC card reader with which contactless IC cards are used: Type A, Type B and Type C; they take different cards for reading and writing depending on the specifications and usage [of the cards]. While Type C is mainstream in Asian countries including Japan, Type A and Type B are mainstream according to the international standard. Note that Type A and Type B are different in amplitude modulation depth (the former 100%, the latter 10%).
It is generally determined whether or not [the card reader] can read and write based on standard cards at the design stage, and it is determined whether or not [the card reader] can read and write by using the actually-used cards at the detail check and evaluation stage.
Even if the contactless IC card is a standard card, some may not be practically used for reading and writing. This is because there are variations in card properties such as the difference in shape or the number of windings of the antenna coil and the difference in the IC chip performance. This may be found particularly in Type B cards in which the amplitude modulation depth is set as low as 10%, as described above.
As a measure to solve such a problem, the resistance at the transmission output unit inside the contactless IC control may be made a variable resistance. By adjusting this variable resistance, the card that is unreadable and unwritable could be made readable and writable. However, it is difficult to determine in advance the precise adjustment of the resistance because the adjustment width of the resistance depends on the loop antenna (antenna coil) of the contactless IC card reader which is to be designed. In other words, [the precise adjustment] is preferably determined based on the contactless IC card which will be actually used or the environment in which the contactless IC card reader is actually installed; however, [the contactless IC card reader] is generally manufactured after the variable resistance value is selected, and therefore, it is difficult to make any changes afterwards.
According to the technology disclosed in the above-described JP 2005-102057 and JP 2006-50406, the modulation depth can be changed afterwards. However, in JP 2005-102057, the phase of the carrier wave contained in the response signal which is received from the contactless IC card needs to be checked for whether or not the modulation depth should be changed (paragraphs [0025] through [0027] of JP 2005-102057); also in JP 2006-50406, the modulation depth needs to be calculated based on the amplitude detected by an amplitude detection circuit (paragraphs [0017] and [0018] in JP 2006-50406); thus, in either case, a longer time may be required for processing. In particular, the demand to shorten the processing time for data reading from the contactless IC card is high compared to the magnetic cards and contact IC cards, demanding faster data reading From the viewpoint of shortening the processing time, JP 2005-102057 needs a data processing using a differential amplifier and level adjustment circuit and JP 2006-50406 needs a data processing that uses the maximum amplitude and the minimum amplitude.